engine temp

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I posted this in another section, I think this is the more appropriate spot so I am deleting the other thread.
i had a weird occurence with my truck this morning. 1987 4x4 silverado 350 tbi. I do not know at what temps the actual guage runs at. It has 4 tick marks. It will rise slightly past the first tick mark until the thermostat opens then drops below the first tick mark. This is the way it has always run. This morning when I hit 70 nph it bounced quickly up and down to the second tick mark. I slowed down and it went to normal. I sped up again and it bounced directly way past the "HOT" it went as far as it could go. It stayed there for roughly 5 to 10 seconds then back to normal. It did this a couple of times. My question is did mmy engine overheat? It was not a gradual bounce it was a very quick eratic almost bounce. Do I have more of an electrical problem? This forum has been very helpfull and I appreciate all of the help
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